DESCRIPTION (From the Applicant's Abstract): Dysregulation of intracellular calcium signaling process has been critically implicated in the pathogenesis of Alzheimer's disease (AD). Notably, disrupting calcium homeostasis can markedly affect formation of each of the hallmark pathological lesions of this insidious disorder: b-amyloid, neurofibrillary tangles, and neuronal cell death. Moreover, calcium dyshomeostasis is an early and highly consistent alteration that occurs in certain earlyonset, autosomal dominant familial AD cases that are caused by mutations in the presenilin (PS1, PS2) genes. Mutations in the presenilin genes cause gain-of-function effects that lead to AD. Thus far, the two most consistent and pathologically significant disturbances associated with mutant presenilin molecules are alterations of proteolysis of proteins such as the b-amyloid precursor protein (APP) and disruption of intracellular calcium signaling processes. Surprisingly, the relationship between APP mismetabolism and calcium dyshomeostasis mediated by mutant presenilins has not been thoroughly investigated, which is the overarching objective of this research application. Toward this end, we propose 5 specific aims that will address the relationship between presenilin-mediated alterations of intracellular calcium signaling and APP proteolysis. Aim 1 will establish if Ab is necessary for presenilin-mediated effects on calcium signaling, by studying cells that contain mutant PS1 but in which the APP gene is eliminated. Aim 2 investigates whether increased A13 formation is sufficient to reproduce the effects of presenilin mutations on calcium signaling by studying primary neurons and cultured cells overexpressing APP. Aim 3 uses cells derived from presenilin knock-out mice to establish the role of endogenous presenilins on calcium signaling. Aim 4 will determine if y-secretase activity is required for the presenilin-mediated effects on calcium signaling by studying cells expressing dominant-negative presenilin mutations (i.e., mutants of the highly conserved transmembrane aspartate residues). Lastly, by manipulating calcium signaling and determining its effects on AB production, aim 5 will address whether the effects of presenilin mutations on calcium signaling are necessary and/or sufficient to increase Ab formation.